Veltman et al., U.S. Pat. No. 4,732,578 discloses an air purification and temperature control system for combat vehicles that incorporates a pressure swing adsorbent system for filtering nuclear, biological and chemical warfare agents. This adsorbent system is comprised of two tanks each of which has an adsorbent bed. As described in column 4, lines 5-45 of Veltman compressed air from the control system enters the first tank through a four way inlet purge valve. Water, hydrocarbons, and chemical agents are adsorbed in the bed and purified so that dry air exits the tank. A portion of the purified air is expanded through an orifice an then passed through the second tank in the direction opposite the flow in the first tank. This flow purges contaminants from the adsorbent bed in the second tank, and is then dumped over board. After a period of time the process is reversed and the second tank receives the compressed air and the first tank is purged.
The Applicants have found that pressure swing adsorbent systems have a number of disadvantages. First, the portion of air required for purging can be as large as half of the air entering the system. By dumping this purging air over board a large amount of energy is lost reducing the system's overall efficiency. Second, if the temperature differential between the air entering the system and the purge air becomes too large, the adsorbent system ability to purify the air starts to degrade.
Accordingly, a need exists for an environmental control systems for ground vehicles and low flying aircraft, that includes a means for filtering nuclear, biological, and chemical warfare agents that does not have the deficiencies associated with pressure swing adsorbent systems.